1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, more particularly to an electrophotographic photosensitive member having improved electrophotographic characteristics.
2. Related Background Art
An electrophotographic photosensitive member of a separate-function type, which comprises different substances each bearing a charge-generating function or a charge-transporting function, has brought about remarkable improvements in sensitivity and durability which had been disadvantages of conventional organic photosensitive members.
Such a separate-function type of electrophotographic photosensitive member is advantageous because the substances for the charge-generating material and the charge-transporting material can be selected respectively from a wide range of substances, which allows easier production of an electrophotographic photosensitive member having desired properties at low cost.
Known charge-transporting materials include pyrazolines as disclosed in Japanese Patent Publication No. 52-4188, hydrazones as disclosed in Japanese Patent Publication Nos. 55-42380 and 55-52063, triphenylamines as disclosed in Japanese Patent Publication 58-32372 and Japanese Patent Application Laid-Open No. 61-132955, and stilbenes as disclosed in Japanese Patent Application Laid-Open Nos. 54-151955 and 58-198043.
Such charge-transporting materials are required (1) to be stable to light and heat, (2) to be stable to ozone, NO.sub.x, and nitric acid which are formed by corona discharge, (3) to have high ability for transporting changes, (4) to have high compatibility with organic solvents and binders, (5) to be produced readily at low cost, and so forth.
Owing to further speed-up and higher quality of images accomplished in recent years, charge-transporting materials are required to satisfy the above requirements at a higher level.